[RE-wrenches] Grid-Connect Inverter with battery, AND auto backoff?

[Troy Harvey]

Load sheding is not a bad idea if the tech exists. Not particularly  
complex either with networkable breakers and a smart controller in the  
inverter. Just software. Cost isn't an issue, they are willing to pay.

The issue on loads isn't battery cut-off (though that isn't a bad  
idea), but shedding the less-important loads to make sure the house  
does exceed the inverter power output. A 6kW inverter subpaneled will  
only give you about four 15 AMP circuits. However a typical house of  
this size will have 30 such circuits, yet good chance it won't be  
drawing much more than 50 AMPs for the whole house at any one time.  
How do you select what is important? Either the inverter is  
complicated or the electricians wiring is complicated.


Troy Harvey
---------------------
Heliocentric
801-453-9434
taharvey at heliocentric.org


On Jun 23, 2009, at 10:01 PM, William Miller wrote:

> Troy:
>
> Let me guess... They want it right away and cheap, too.  Generally  
> speaking, this is an impractical request.  Electrically operated  
> circuit breakers or 20 A relays and controllers are expensive and  
> complicated.  One thing to learn in this trade is when to try and  
> talk a client out of a bad idea, and when a client has such wacky  
> ideas that it is best to walk away.
>
> I could, however, suggest two ways to do this:
>
> 1. Use two inverters and set the LBCO for one high.  Connect one to  
> critical loads and one (with the high LBCO) to non-critical loads.   
> When the batteries start getting low, the non-critical-loads  
> inverter shuts down, leaving the critical-loads inverter running.
>
> Realize that you now need four load centers:  Grid, generator (you  
> have recommended a generator so they can use their wide screen TV  
> during a wind storm, correct?), non-critical loads and critical  
> loads.  This type of design gets complicated fast.  Will the AHJ be  
> able to track this?  Set a clause that allows you to collect hourly  
> fees when they require three different meetings and three re-writes  
> of the permit application.
>
> 2. Use an Outback with external relays to shut off loads when the  
> battery voltage falls below a certain point.   This is a crude  
> approach, the parameters are not flexible (hard coded delay values)  
> and it requires custom built relay panels, time consuming, expensive  
> and a potential service problem.
>
> Either system is actuated on battery voltage rather than loads.   
> Inverters I am familiar with have relays and internal controls that  
> operate based a set-able battery voltages, but I know of none that  
> has a programmable relay to actuate at a certain load level.  In  
> addition, loads change so rapidly that this type of switching would  
> be erratic.  Loading is a component of battery voltage, anyway, so  
> you are including that indirectly.
>
> Good Luck,
>
> William Miller
>
>
>
> At 07:41 PM 6/23/2009, you wrote:
>> Hi folks,
>>
>> I need an inverter/charger/controller solution for a grid connect
>> house that:
>> 1. grid-connects (net-meters)
>> 2. Islands off of the battery in outages (whole house UPS)
>> 3. Feeds into the whole house breaker, so the whole house is backed  
>> up
>> 4. Shuts down less important breakers as needed, if the load for the
>> whole house is over the inverter limit
>>
>> Instead of guessing which breakers are important to put on a battery
>> backed up sub-panel, my client would like the whole house backed up.
>> But of course, can't guarantee that the house won't be drawing too
>> much for a 6000 Watt inverter at any given time. So would like to  
>> have
>> the system intelligently remove less important breakers until the
>> system is below the inverter operation wattage.
>>
>> Anyone know of a inverter system that is smart like that?
>>
>> Troy Harvey
>> ---------------------
>> Heliocentric
>> 801-453-9434
>> taharvey at heliocentric.org
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